The present invention relates generally to improved methods and apparatus for testing electrical circuit cards or boards having different patterns of test points. An electrical circuit board or card may typically contain integrated circuits, resistors, printed circuits, etc.
As exemplified by U.S. Pat. Nos. 3,016,489; 3,757,219; 3,654,585 and 4,164,704, various circuit board testing apparatus are known whereby an array of contact probes (connected to test apparatus) are urged into contact with the conductive test points of a circuit board which is to be tested.
One advantageous approach has been to employ a test fixture containing an array of spring-loaded contacts which are forced into contact with the test points of a circuit board by creating a vacuum between the board and fixture. The use of a vacuum has the advantage of creating a uniform distribution of force across the board. In order to provide for testing boards having different patterns of test points, the test fixture is typically provided with sufficient spring-loaded contact probes to accommodate a number of different test point patterns. A personalizing board or the like is then employed for each different type of circuit board to be tested to select the desired probe pattern which is to be used for that circuit board. However, since each spring-loaded probe is typically loaded with a 4 ounce to 8 ounce spring, and since the vacuum can provide a force on the contact probes of no greater than ambient pressure (about 14 pounds per square inch), the number of spring-loaded probes which can be provided per square inch is limited, which in turn limits the number of different types of boards which can be tested by a vacuum-type test fixture.
Known vacuum-type circuit board test fixtures have attempted to circumvent the above described limitation on the number of spring-loaded contact probes that can be provided by providing different types of contact probe arrays, or by providing for removing probes that are not needed, or by providing expensive personalizing boards that obviate the need for the vacuum to depress unused probes. However, these approaches are cumbersome and/or expensive.